The first-principles plane-wave supersoft pseudopotential method based on the density functional theory (DFT-D) is used to determine the optical CO gas-sensing properties of pure, single-doped N, single-doped Rh, and N/Rh codoped rutile TiO₂ (110) surfaces. We observe that the pure and doped surfaces of rutile TiO₂ exhibit certain optical CO gas-sensing characteristics that results from variations in surface oxidation performance. We find that N/Rh codoping greatly improves surface oxidation. The adsorption of CO gas on an N/Rh co-doped surface is characterized by a negligent adsorption distance, enormous adsorption energy, and unparalleled stability after adsorption; it is also easy to implement. Therefore, N/Rh co-doped surfaces are more effective at optical gas sensing when compared with pure and single-doped surfaces, and N/Rh codoping is a suitable way to improve the optical gas-sensing properties of TiO₂.